There are two main types of gutter systems: external and internal. Aesthetics aside, the major difference between the two styles involves what happens when the gutter fails. Gutter failure can occur from something as simple as a clogged downspout or as complex as extreme rainfall that exceeds what the system was designed to carry.
External gutter systems commonly involve installing a gutter at the low end (or eave) of the roof outside the building footprint. Downspouts are then connected to the gutter and allow any water that flows into the gutter to drain outside of the building.
Conversely internal gutter systems function by funneling water to a series of troughs within the roof system. These troughs then drain water into tubes located inside of the building.
At first blush, this difference may seem minor but the implications can be potentially serious.
While internal gutter systems aren’t necessarily rare, it’s routinely recommended to avoid them if at all possible. The reasons for this recommendation are numerous.
First, as mentioned earlier, internal gutters deposit water inside the building envelope. When the tube drainage system fails to function properly, water infiltration can lead to serious damage to the building infrastructure and occupants below in a variety of ways:
Consequently, whenever possible, it’s preferred to use designs that allow water to exit outside of the building envelope.
Secondly, internal gutters can be incredibly difficult to repair or replace because the roofing material is commonly installed on top of the gutter system. When shorter life roofing systems, such as membranes and TPO systems, utilize an internal gutter, replacement of the gutter is less critical as they tend to wear out at the same pace as the roofing system.
However, when internal gutter systems are used with long life products such as metal roofing, which can routinely last 50-60 years, internal gutter repair or replacement can become a major issue.
In fact, owners often find themselves replacing roofing material which is still functional simply to address internal gutter replacement. Consequently, internal gutter systems should be avoided if at all possible in metal roofing projects.
For projects where an internal gutter cannot be avoided, consider the following tips:
In summary, internal gutters have been in use for centuries so it’s clear they “can” work. But it’s also clear they represent a big risk of failure that’s better avoided whenever possible.
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